A Foraging Cost of Migration for a Partially Migratory Cyprinid Fish

Migration has evolved as a strategy to maximise individual fitness in response to seasonally changing ecological and environmental conditions. However, migration can also incur costs, and quantifying these costs can provide important clues to the ultimate ecological forces that underpin migratory behaviour. A key emerging model to explain migration in many systems posits that migration is driven by seasonal changes to a predation/growth potential (p/g) trade-off that a wide range of animals face. In this study we assess a key assumption of this model for a common cyprinid partial migrant, the roach Rutilus rutilus, which migrates from shallow lakes to streams during winter. By sampling fish from stream and lake habitats in the autumn and spring and measuring their stomach fullness and diet composition, we tested if migrating roach pay a cost of reduced foraging when migrating. Resident fish had fuller stomachs containing more high quality prey items than migrant fish. Hence, we document a feeding cost to migration in roach, which adds additional support for the validity of the p/g model of migration in freshwater systems.

Fixed and Flexible: Coexistence of Obligate and Facultative Migratory Strategies in a Freshwater Fish

Migration is an important event in many animal life histories, but the degree to which individual animals participate in seasonal migrations often varies within populations. The powerful ecological and evolutionary consequences of such partial migration are now well documented, but the underlying mechanisms are still heavily debated. One potential mechanism of partial migration is between-individual variation in body condition, where animals in poor condition cannot pay the costs of migration and hence adopt a resident strategy. However, underlying intrinsic traits may overrule such environmental influence, dictating individual consistency in migratory patterns. Unfortunately, field tests of individual consistency compared to the importance of individual condition on migratory propensity are rare. Here we analyse 6 years of field data on roach migration, gathered by tagging almost 3000 individual fish and monitoring their seasonal migrations over extended periods of time. Our aims were to provide a field test of the role of condition in wild fish for migratory decisions, and also to assess individual consistency in migratory tendency. Our analyses reveal that (1) migratory strategy, in terms of migration/residency, is highly consistent within individuals over time and (2) there is a positive relationship between condition and the probability of migration, but only in individuals that adopt a migratory strategy at some point during their lives. However, life-long residents do not differ in condition to migrants, hence body condition is only a good predictor of migratory tendency in fish with migratory phenotypes and not a more general determinant of migratory tendency for the population. As resident individuals can achieve very high body condition and still remain resident, we suggest that our data provides some of the first field evidence to show that both facultative and obligate strategies can co-exist within populations of migratory animals.

Wingless activity in the precursor cells specifies neuronal migratory behavior in the Drosophila nerve cord.

Neurons and their precursor cells are formed in different regions within the developing CNS, but they migrate and occupy very specific sites in the mature CNS. The ultimate position of neurons is crucial for establishing proper synaptic connectivity in the brain. In Drosophila, despite its extensive use as a model system to study neurogenesis, we know almost nothing about neuronal migration or its regulation. In this paper, I show that one of the most studied neuronal pairs in the Drosophila nerve cord, RP2/sib, has a complicated migratory route. Based on my studies on Wingless (Wg) signaling, I report that the neuronal migratory pattern is determined at the precursor cell stage level. The results show that Wg activity in the precursor neuroectodermal and neuroblast levels specify neuronal migratory pattern two divisions later, thus, well ahead of the actual migratory event. Moreover, at least two downstream genes, Cut and Zfh1, are involved in this process but their role is at the downstream neuronal level. The functional importance of normal neuronal migration and the requirement of Wg signaling for the process are indicated by the finding that mislocated RP2 neurons in embryos mutant for Wg-signaling fail to properly send out their axon projection.

STAT3 CONTROLS THE NEUTROPHIL MIGRATORY RESPONSE TO CXCR2 AND ITS LIGAND MIP-2 (CXCL2)

Among the first white blood cells to respond to bacterial and fungal infections, neutrophils are produced in the bone marrow, released into circulating blood, and recruited to inflamed tissue. The cytokine granulocyte colony-stimulating factor (G

To boldly go: individual differences in boldness influence migratory tendency

Partial migration, whereby only a fraction of the population migrates, is thought to be the most common type of migration in the animal kingdom, and can have important ecological and evolutionary consequences. Despite this, the factors that influence which individuals migrate and which remain resident are poorly understood. Recent work has shown that consistent individual differences in personality traits in animals can be ecologically important, but field studies integrating personality traits with migratory behaviour are extremely rare. In this study, we investigate the influence of individual boldness, an important personality trait, upon the migratory propensity of roach, a freshwater fish, over two consecutive migration seasons. We assay and individually tag 460 roach and show that boldness influences migratory propensity, with bold individuals being more likely to migrate than shy fish. Our data suggest that an extremely widespread personality trait in animals can have significant ecological consequences via influencing individual-level migratory behaviour.

Sizing up your enemy: individual predation vulnerability predicts migratory probability

Partial migration, in which a fraction of a population migrate and the rest remain resident, occurs in an extensive range of species and can have powerful ecological consequences. The question of what drives differences in individual migratory tendency is a contentious one. It has been shown that the timing of partial migration is based upon a trade-off between seasonal fluctuations in predation risk and growth potential. Phenotypic variation in either individual predation risk or growth potential should thus mediate the strength of the trade-off and ultimately predict patterns of partial migration at the individual level (i.e. which individuals migrate and which remain resident). We provide cross-population empirical support for the importance of one component of this model—individual predation risk—in predicting partial migration in wild populations of bream Abramis brama, a freshwater fish. Smaller, high-risk individuals migrate with a higher probability than larger, low-risk individuals, and we suggest that predation risk maintains size-dependent partial migration in this system.

Effects of Lipophilic Extract of Viscum album L. and Oleanolic Acid on Migratory Activity of NIH/3T3 Fibroblasts and on HaCat Keratinocytes

Viscum album L. lipophilic extract (VALE) contains pharmacologically active pentacyclic triterpenes that are known to exhibit immunomodulatory, antitumor, and wound healing activity. Preliminary clinical observations indicate that VALE was able to influence cutaneous wound healing in vivo. The objective of this study was to investigate wound closure related properties of VALE in vitro. As measured in a wound healing assay, VALE and its predominant triterpene oleanolic acid (OA) significantly and dose dependently promoted the migration of NIH/3T3 fibroblasts in vitro, thereby leading to an enhanced wound closure. Compared to the negative control, maximal stimulation by 26.1% and 26.2%, respectively, was attained with 10 μg/mL VALE and 1 μg/mL OA. Stimulation of proliferation in NIH/3T3 fibroblasts by VALE and OA could be excluded. At higher concentrations both substances affected proliferation and viability of NIH/3T3 fibroblasts and HaCat keratinocytes. In the toxic range of concentrations of VALE and OA, migration of NIH/3T3 fibroblasts was suppressed. The extent of the stimulatory effect on cell migration of VALE quite closely corresponded to the effect expected by the concentrations of OA contained in the crude extract VALE. These data support the casual observation that Viscum album L. lipophilic extract might modulate wound healing related processes in vivo.

The Effects of Smolt Stocking Strategies on Migratory Path Selection of Adult Atlantic Salmon in the Penobscot River, Maine

Understanding the homing behavior of Atlantic salmon Salmo salar is vital to the restoration program employed on the Penobscot River, Maine. To produce significant adult returns, managers currently stock hatchery-raised smolts in specific river sections, providing smolts the opportunity to imprint on chemical signals and enabling their return to productive spawning and rearing habitat as adults. In this study, we used observational evidence from passive integrated transponder telemetry to determine whether adults returning from smolt stockings behaved in a way that suggested strong homing to smolt stocking locations. Adults returning from smolt stocking locations located in or at the mouth of the Piscataquis River were more likely to be detected as entering the Piscataquis River than were adults returning from the upper Penobscot River smolt stocking locations. In general, returning adult Atlantic salmon that had been stocked near or in tributaries as smolts chose a path more quickly than those that had been stocked in more downstream or main-stem locations. These results suggest that Atlantic salmon smolts should be stocked at specific sites with superior habitat for spawning kind juvenile survival to capitalize on the strong homing tendency in adults. This technique call also be utilized to allow for natural selection and the development of localized stocks.

Migratory Urge and Gill Na(+),K(+)-ATPase Activity of Hatchery-Reared Atlantic Salmon Smolts from the Dennys and Penobscot River Stocks, Maine

Hatchery-reared Atlantic salmon Salmo salar smolts produced from captive-reared Dennys River and sea-run Penobscot River broodstock are released into their source rivers in Maine. The adult return rate of Dennys smolts is comparatively low, and disparity in smolt quality between stocks resulting from genetic or broodstock rearing effects is plausible. Smolt behavior and physiology were assessed during sequential 14-d trials conducted in seminatural annular tanks with circular flow. "Migratory urge'' (downstream movement) was monitored remotely using passive integrated transponder tags, and gill Na(+),K(+)-ATPase activity was measured at the beginning and end of the trials to provide an index of smolt development. The migratory urge of both stocks was low in early April, increased 20-fold through late May, and declined by the end of June. The frequency and seasonal distribution of downstream movement were independent of stock. In March and April, initial gill Na(+),K(+)-ATPase activities of Penobscot River smolts were lower than those of Dennys River smolts. For these trials, however, Penobscot River smolts increased enzyme activity after exposure to the tank, whereas Dennys River smolts did not, resulting in similar activities between stocks at the end of all trials. There was no clear relationship between migratory urge and gill Na(+),K(+)-ATPase activity. Gill Na(+),K(+)-ATPase activity of both stocks increased in advance of migratory urge and then declined while migratory urge was increasing. Maximum movement was observed from 2 h after sunset through 1 h after sunrise but varied seasonally. Dennys River smolts were slightly more nocturnal than Penobscot River smolts. These data suggest that Dennys and Penobscot River stocks are not markedly different in either physiological or behavioral expression of smolting.

Modulation of In Vivo Migratory Function of α2β1 Integrin in Mouse Liver

We report herein that expression of α2β1 integrin increased human erythroleukemia K562 transfectant (KX2C2) cell movement after extravasation into liver parenchyma. In contrast, a previous study demonstrated that α2β1 expression conferred a stationary phenotype to human rhabdomyosarcoma RD transfectant (RDX2C2) cells after extravasation into the liver. We therefore assessed the adhesive and migratory function of α2β1 on KX2C2 and RDX2C2 cells using a α2β1-specific stimulatory monoclonal antibody (mAb), JBS2, and a blocking mAb, BHA2.1. In comparison with RDX2C2 cells, KX2C2 were only weakly adherent to collagen and laminin. JBS2 stimulated α2β1-mediated interaction of KX2C2 cells with both collagen and laminin resulting in increases in cell movement on both matrix proteins. In the presence of Mn2+, JBS2-stimulated adhesion on collagen beyond an optimal level for cell movement. In comparison, an increase in RDX2C2 cell movement on collagen required a reduction in its adhesive strength provided by the blocking mAb BHA2.1. Consistent with these in vitro findings, in vivo videomicroscopy revealed that α2β1-mediated postextravasation cell movement of KX2C2 cells in the liver tissue could also be stimulated by JBS2. Thus, results demonstrate that α2β1 expression can modulate postextravasation cell movement by conferring either a stationary or motile phenotype to different cell types. These findings may be related to the differing metastatic activities of different tumor cell types.

Frequency of migrants and migratory activity are genetically correlated in a bird population: Evolutionary implications

Most migratory bird populations are composed of individuals that migrate and individuals that remain resident. While the role of ecological factors in maintaining this behavioral dimorphism has received much attention, the importance of genetic constraints on the evolution of avian migration has not yet been considered. Drawing on the recorded migratory activities of 775 blackcaps (Sylvia atricapilla) from a partially migratory population in southern France, we tested two alternative genetic models about the relationship between incidence and amount of migratory activity. The amount of migratory activity could be the continuous variable “underlying” the phenotypic expression of migratory urge, or, alternatively, the expression of both traits could be controlled by two separate genetic systems. The distributions of migratory activities in five different cohorts and the inheritance pattern derived from selective breeding experiments both indicate that incidence and amount of migratory activity are two aspects of one trait. Thus, all birds without measurable activity have activity levels at the low end of a continuous distribution, below the limit of expression or detection. The phenotypic dichotomy “migrant–nonmigrant” is caused by a threshold which may not be fixed but influenced both genetically and environmentally. This finding has profound implications for the evolution of migration: the transition from migratoriness to residency should not only be driven by selection favoring resident birds but also by selection for lower migratory activity. This potential for selection on two aspects, residency and migration distance, of the same trait may enable extremely rapid evolutionary changes to occur in migratory behavior.

Natal origins of migratory monarch butterflies at wintering colonies in Mexico: New isotopic evidence

Each year, millions of monarch butterflies from eastern North America migrate to overwinter in 10–13 discrete colonies located in the Oyamel forests of central Mexico. For decades efforts to track monarch migration have relied on observations and tag-recapture methods, culminating with the discovery of the wintering colonies in 1975. Monarch tag returns from Mexico, however, are few and primarily from two accessible colonies, and therefore tag-recapture techniques have not quantified natal origins or distinctiveness among monarch populations at wintering sites. Such information would be invaluable in the conservation of the monarch and its migration phenomenon since the wintering sites currently are threatened by habitat alteration. Here we show that stable hydrogen (δD) and carbon (δ13C) isotope ratios of wintering monarchs can be used to evaluate natal origins on the summer breeding range. Stable-hydrogen and carbon isotopic values of 597 wintering monarchs from 13 wintering roost sites were compared with isotopic patterns measured in individuals at natal sites across their breeding range over a single migration cycle. We determined that all monarch wintering colonies were composed of individuals originating mainly from the Midwest, United States, thereby providing evidence for a panmictic model of wintering colony composition. However, two colonies showed more northerly origins, suggesting possible priority colonies for conservation efforts.

Variation in the expression of migratory activity in blackcap (Sylvia atricapilla); effects of the origin, environmental conditions, dominance and personalities

La migración es una respuesta a cambios estacionales del clima generando desplazamientos periódicos entre hábitats de cría y de invernada, permitiendo así el uso temporal de los recursos disponibles. La migración implica unos costes energéticos muy elevados, un aumento de la depredación potencial, variaciones ambientales y una disponibilidad de alimento impredecible a lo largo de la ruta migratoria; por lo que es una de las actividades más desafiantes de su ciclo vital. A pesar de ello, los beneficios de la migración compensan sus costes. La migración está programada genéticamente, siendo relativamente constante en su momento, distancia y dirección. Por otro lado, ambiente juega un papel predominante en algunas poblaciones, pudiendo modificar el comportamiento migratorio de una estrategia parcial o facultativa a un modo de vida sedentario. Con el fin de describir el origen y evolución del comportamiento migratorio en aves, se ha propuesto un “modelo de umbral” genético para determinar si un ave es migrante o sedentaria. Dentro de una variable continua (p.ej. la concentración de proteínas u hormonas), este modelo asume que existe una actividad migratoria subyacente implicada en su expresión génica. Este umbral divide cada variable en categorías dicotómicas que definen el fenotipo de un individuo. Los ejemplares sin actividad migratoria muestran valores por debajo de este umbral, siendo clasificados como sedentarios, mientras que los ejemplares migrantes muestran valores por encima del umbral definido. Los cambios de estrategia vital no dependen únicamente de la posición del umbral determinado genéticamente sino también de las variables ambientales, por lo que dichas variaciones deben ser añadidas al modelo. Este modelo de umbral ambiental predice que el carácter migratorio de los individuos situados en los extremos de distribución no se encuentra afectado por los factores ambientales, mientras que aquellos más próximos al umbral pueden más fácilmente cambiar su estrategia migratoria...